There are many different types of bicycle chainwheel and crank assemblies which are currently available for bicycles. One example of a chainwheel and crank arm is disclosed in Japanese Utility Model Publication 32-14512. This Japanese Publication discloses a three piece chainwheel plate in which the crank connecting arms and the sprockets are coupled together by rivets. Such chainwheel plates have a crank arm with a pedal at its tip, three arm components extending radially in three directions from the base of the crank arm, V-shaped end portions riveted to the tips of the arm components, and two sprockets or chainwheel components of different sizes coupled to the V-shaped end portions. The tips of the V-arms are riveted to the sprockets. Chainwheel plates that are riveted to the sprockets have higher rigidity during rotation than do sprockets bolted to chainwheel plates.
In the aforementioned conventional chainwheel plate, the three arm portion and V-shaped end portions are coupled together by riveting, which concentrates the stress in this portion during rotation. Also, in cases in which affixing is accomplished using three rivets, it is difficult to uniformly distribute force among the three rivets if holes have not been bored sufficiently accurately. Furthermore, the force increases because the rivet connection area lies to the inside of the action point of the force when reaction from the chain is applied to the sprocket. As a result, an attempt to maintain proper rigidity results in larger rivet diameters and an increased weight.
In view of the above, it will be apparent to those skilled in the art that there exists a need for an improved crank set and/or chainwheel plate with high rigidity and minimal weight. This invention addresses this need in the art as well as other needs which will become apparent to those skilled in the art from this disclosure.